Dynamic-chemical coupling of the upper troposphere and lower stratosphere region

The importance of the interaction between chemistry and dynamics in the upper troposphere and lower stratosphere for chemical species like ozone is investigated using two chemistry-climate models and a Lagrangian trajectory model. Air parcels from the upper troposphere, i.e. regions of lightning and aircraft emissions, are able to be transported into the lowermost stratosphere (LMS). Trajectory calculations suggest that the main transport pathway runs via the inter tropical convergence zone, across the tropical tropopause and then to higher latitudes, i.e. into the LMS. NOx from aircraft emissions at mid-latitudes are unlikely to perturb the LMS since they are washed-out while still in the troposphere. In contrast, NOx from tropical lightning has the chance to accumulate in the LMS. Because of the longer residence times of NOx in the LMS, compared to the upper troposphere, this excess NOx from lightning has the potential to form ozone in the LMS, which then is transported back to the troposphere at mid-latitudes. In the models, around 10% of the ozone concentration and 50% of the NOx concentration in the northern hemisphere LMS is produced by lightning NOx At least 5% of the ozone concentration and 35% the NOx concentration at 150 hPa at mid-latitudes originates from tropical lightning in the climate-chemistry simulations.     

Climate forcing by the on-road transportation and power generation sectors

The on-road transportation (ORT) and power generation (PG) sectors are major contributors to carbon dioxide (CO₂) emissions and a host of short-lived radiatively-active air pollutants, including tropospheric ozone and fine aerosol particles, that exert complex influences on global climate. Effective mitigation of global climate change necessitates action in these sectors for which technology change options exist or are being developed. Most assessments of possible energy change options to date have neglected non-CO₂ air pollutant impacts on radiative forcing (RF). In a multi-pollutant approach, we apply a global atmospheric composition-climate model to quantify the total RF from the global and United States (U.S.) ORT and PG sectors. We assess the RF for 2 time horizons: 20- and 100-year that are relevant for understanding near-term and longer-term impacts of climate change, respectively. ORT is a key target sector to mitigate global climate change because the net non-CO₂ RF is positive and acts to enhance considerably the CO₂ warming impacts. We perform further sensitivity studies to assess the RF impacts of a potential major technology shift that would reduce ORT emissions by 50% with the replacement energy supplied either by a clean zero-emissions source (S1) or by the PG sector, which results in an estimated 20% penalty increase in emissions from this sector (S2). We examine cases where the technology shift is applied globally and in the U.S. only. The resultant RF relative to the present day control is negative (cooling) in all cases for both S1 and S2 scenarios, global and U.S. emissions, and 20- and 100-year time horizons. The net non-CO₂ RF is always important relative to the CO₂ RF and outweighs the CO₂ RF response in the S2 scenario for both time horizons. Assessment of the full impacts of technology and policy strategies designed to mitigate global climate change must consider the climate effects of ozone and fine aerosol particles.     

Drivers and constraints of waste-to-energy incineration for sustainable municipal solid waste management in developing countries

Journal of Material Cycles and Waste Management - Implementation of waste-to-energy (WtE) incineration has recently surged in developing countries, but the drivers of this growth and the...